1. Field of the Invention
This invention relates to a method of forming epitaxial layers on substrate materials and, more particularly, to a method of forming semiconductor epitaxial layers on semiconductor wafers.
2. Description of the Prior Art
In the production of semiconductor devices including transistors and integrated circuits, an important and basic process is the formation of epitaxial layers on monocrystalline semiconductor wafer substrates. Although the process of epitaxial layer formation, particularly with respect to silicon semiconductor material, is highly developed, a problem arises which still prevents the realization of the near perfection which seems inherently possible with monocrystalline semiconductor material.
In particular, during the formation of epitaxial layers of pyrolytic decomposition processes at relatively high temperatures, radiation from the rim and peripheral edge surface of the wafer substrate reduces the temperature in that portion in comparison to central portions of the wafer surface. These temperature gradients produce internal stresses during epitaxial crystal growth which cause imperfections termed slip dislocations. Moreover, these dislocations tend to propagate through the deposited epitaxial film following patterns determined by the crystallographic orientation of the substrate surface. Although the material remains a single crystal, the presence of these slip dislocations affects the quality of the subsequently produced semiconductor devices, generally resulting in electrically degraded PN junctions.
The presence of slip dislocations reduces the yield of satisfactory semiconductor devices from such a wafer. Devices coincident with portions of the wafer containing such dislocations will generally be unsatisfactory and must be discarded.
Accordingly, an object of this invention is a method of inhibiting slip dislocation during the epitaxial deposition process.